1. Field of the Invention
The present invention relates to a process for preparing at a stroke a saturated/unsaturated mixed fatty acid ester sulfonate, that is, a mixture of a saturated fatty acid ester sulfonate and an unsaturated fatty acid ester sulfonate.
A saturated fatty acid ester sulfonate and an unsaturated fatty acid ester sulfonate are valuable as surface active agents even when used alone, but a mixture of both sulfonates is almost ideal as an active ingredient of a detergent because the mixture has an excellent foaming property, cleansing power and permeating property, and a good rinsing property.
2. Description of the Related Art
As a most common means for preparing a saturated/unsaturated mixed fatty acid sulfonate having the above-mentioned characteristics, there is considered a process comprising sulfonating a mixture of a saturated fatty acid ester and an unsaturated fatty acid ester (hereinafter referred to as a saturated/unsaturated mixed fatty ester). However, the saturated fatty acid ester and the unsaturated fatty acid ester are greatly different in their reactivity to sulfonation, namely, the reactivity of the unsaturated fatty acid ester is higher than that of the saturated fatty acid ester. Accordingly, when a mixture of both esters is sulfonated according to a customary procedure, the unsaturated fatty acid ester is preferentially sulfonated, and if the reaction is continued until the saturated fatty acid ester is sulfonated, the unsaturatd fatty acid ester is polysulfonated and the color of the reaction product is degraded. If sulfonation is carried out under mild conditions such that degradation of the color of the product can be avoided, a satisfactory conversion cannot be attained with respect to the saturated fatty acid ester.
Accordingly, when a saturated/unsaturated mixed fatty acid ester sulfonate is desired, a process is inevitably adopted in which the respective fatty acid esters are independently sulfonated and the respective sulfonation products are neutralized, and the thus-obtained sulfonates are then mixed. When a saturated fatty acid ester alone is used, sulfonation can be accomplished relatively easily according to a process as disclosed in Japanese Examined Patent Publication Nos. 39-20482, 39-28635 or 41-965. However, in the case of an unsaturated fatty acid ester, because of the high reactivity, control of the reaction conditions is difficult, and if a known process as disclosed in the above patent publications is adopted, it is impossible to obtain a light-color sulfonation product in a high yield.
Note, the specification of British Patent No. 1,278,421 discloses a process for the film sulfonation of an unsaturated fatty acid. However, if this process is applied to the sulfonation of an unsaturated fatty acid ester, it is impossible to obtain a light-color sulfonation product in a high yield.